Radio receiving system



V V 7 Examiner j/ 3 July 28, 1942 w, HA EN 2,290,959

RADIO RECEIVING SYSTEM Filed April 9, 1941 Patented July 28, 1942 Examiner UNITED STATES PATENT OFFICE RADIO RECEIVING SYSTEM Wolfgang Hagen, Berlin, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a company Application April 9, 1941, Serial No. 387,671 In Germany March 13, 1940 3 Claims.

This invention relates to radio systems in which broadcast or wired radio receivers have a supply equipment common to them, namely, a receiving antenna or a wired radio sender, respectively.

Receivers so arranged require to be provided with a neutralizing arrangement intended to prevent disturbances, such as reaction singing, which may arise in any one of the receivers, from acting on the other receivers. This neutralizing arrangement should be such as to minimize the attenuation it exerts upon the useful energy arriving from the common antenna or the common radio sender, as the case may be.

The invention will be understood from the following description, reference being had to the accompanying drawing, in which Fig. 1 is a diagram showing a prior arrangement, while Fig. 2 is a diagram representing an embodiment of the invention.

A denotes receivers of which only two are shown by rectangles. The receivers A are joined to points a, b of the supply equipment over resistances Ra. Re is the input resistance of each receiver. If Ra=Re then the useful voltage undergoes an attenuation in the ratio 1:2. For instance, in the case of ten receivers A the loading resistance of the supply equipment is For obtaining the maximum efliciency the output resistance of the supply equipment must be made to approach the value Ra "5 so that The disturbing attenuation acting from a receiver on another hence corresponds to the value The useful voltage at the supply equipment has been assumed to be to 20 mv., mv. being the symbol for millivolts, that is to say, the receiver is supplied with 5 to 10 mv. The feedback voltage of one receiver may amount to about 2 v. The disturbing voltage at the other receivers then amounts to It will thus be seen that the disturbing voltage is many times greater than the useful voltage. In order to overcome this drawback, the resistance of the supply equipment at Rs may be made small. This expedient, however, involves a great expenditure in transmitting power.

According to the invention the attenuation of the disturbing voltage is increased by short-circuiting the disturbing receiver with the aid of a voltage-controlled resistance.

In order to achieve this, the arrangement illustrated in Fig. 2 may be adopted. The voltagecontrolled resistances are here shown to be rectifiers G1, G2. These rectifiers are connected in parallel with the receivers A and are so chosen that with the incoming small useful voltage of about 10 mv. their resistance is high compared with Re. With increasing voltage the resistances become less and thus act to load the receiver increasingly. The rectifiers in this way absorb excess of power. In the event of feedback connection of a receiver, the rectifiers joined to this receiver decrease in resistance to such extent that the feedback voltage becomes ineffective so as not to disturb the other receivers. Th de mand upon the supply equipment at Rs is not augmented appreciably through the short-circuiting since the resistances Ra prevent short-circuiting of Rs. As will be understood from Fig. 2 two rectifiers of opposite polarities are connected in parallel in order uniformly to limit the two half-waves of the alternating voltage. When the small useful amplitude is received the resistance of the rectifiers is high compared with Re. As a result no rectifier effect occurs, that is to say, the frequencies of the incoming programs are not modulated with each other. It will thus be seen that the programs are not affected in any way.

While for simplicity Fig. 2 shows two rectifiers as limiting devices it is to be understood that any other suitable non-linear limiting resistances may be employed instead. The aim should be to provide for a limiting action not efiective in the case of the incoming useful amplitude. The limiting action should be such as to limit only the disturbing amplitude outgoing from a receiver or to prevent the receiver from being overmodulated by the disturbing voltage being too great.

What is claimed is:

1. In a high frequency signal distribution system of the type having a plurality of high frequency receivers which are subject to self-generating disturbances such as self-reaction singing of a higher level than the signals to be received, a common source of high frequency signals for supplying all said receivers, and means to prevent the disturbances in one receiver from interfering with the normal reception of signals by the other receivers, the last-mentioned means comprising a voltage-dependent resistor in shunt to the input of each receiver, and an isolating resistor connected between each said voltagedependent resistor and said common source.

2. A system according to claim 1 in which said voltage-dependent resistor is formed of two nonlinear resistances connected in opposition to each other.

3. A system according to claim 1 in which said voltage-dependent resistor comprises a pair of oppositely connected rectifiers which do not exert any substantial rectifying effect except at the relatively high level of said disturbances.

WOLFGANG HAGEN. 

